This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to patent application Serial No. MI2002A 000785 filed in Italy on Apr. 12, 2002, the entire content of which is hereby incorporated by reference.
The present invention relates to a device and a method for supplying electric energy to functions located onboard of the carriages of a sorting machine, such device being adapted to acquire mechanical energy from the drafting system of said sorting machine and transform it into electric energy.
Such method also provides for the use of the kinetic energy of the same machine as an accumulator from which power may be drawn for short peaks of strong electrical consumption that could sometimes occur.
An object of the present invention is mainly applied to xe2x80x9cCross Beltxe2x80x9d sorting machines. These machines consist of an endless train of carriages moving constantly along a path going from the item input stations to the devices for collecting sorted items. The term xe2x80x9cCross Beltxe2x80x9d indicates that the item-sorting unit with which the carriage is equipped is a small conveyor belt capable of moving independently, by an electric motor, in either of two directions orthogonal to the running direction of the sorting machine. See, for example, the sorting machines disclosed in U.S. Pat. Nos. 5,803,230, 6,209,703 and 6,253,904, the disclosures of which are incorporated herein by reference.
Such sorting machine is therefore usually activated during the item loading step to bring the same items onboard, and in the unloading step, in one or both directions, to deliver the items to the appropriate destination. The energy required to actuate the conveyor belt is provided by an electric motor onboard of each carriage. The mean power required of a machine for sorting carried items, that is, for activating the motors that actuate the conveyor belts onboard of the carriages, is in the range of 2-3 kW on the overall. However, due to concurrent belt activation, e.g., during unloading, which is possible based on probabilistic combinations relating to the destinations of the items being sorted, electric power peaks of more than 20 kW may sometimes be required for short times.
Of course, it would be advantageous to size the power supply system on the basis of mean power, rather than peak power.
Several methods and devices are known in the prior art which are adapted to transfer, onboard of the train of carriages, the electric energy required to operate the motors drafting the conveyor belts.
A known method for transferring electric energy onboard of the train of carriages consists in a system of busways arranged along the machine and powered by several feeders (typically 70 V, 100 A). Onboard of some carriages there are sliding contacts that allow drawing the energy that will be transferred to the other carriages by wiring arranged along the entire train of carriages. Such solution is technically valid and widely tested, but it exhibits some technical disadvantages. In the first place, it is expensive because the busways, which are made of copper, must be arranged perfectly parallel to the machine. Moreover, if they are loose, they vibrate and cause the breaking of the sliding contacts. In turn, also sliding contacts are expensive since they consist of pantographs that are difficult to implement; moreover, the electrical contacts are subject to wear and to accidental breakage.
Another known method consists in the inductive transmission of electric energy. A pair of wires, forming one or more maxi-turns along the entire machine, forms a closed circuit in which a generator transmits an alternate current of 50-100 A at an approximate frequency of 28 kHz. The current flowing into the two wires generates a concentric magnetic field around the two wires. The E-core of transformers installed on the carriages faces the two wires, thereby closing the magnetic circuit. An alternate current is induced through the turns wound on such core, and it can be straightened and used for powering the onboard motor. Such solution is conceptually simple but it exhibits two serious disadvantages. In the first place, high frequencies induce parasitic currents in metal items placed nearby, so it is necessary to set up suitable protection to prevent attenuation problems and potentially hazardous situations for maintenance personnel. In addition, the solution is not very efficient and does not allow transferring the necessary peak powers, and therefore it implies the need using onboard accumulators to deliver strong current peaks, when required.
Another known method consists in drawing the mechanical energy from the drafting system, for example by a pressure wheel mounted on each carriage, which keeps the machine working at constant speed. The mechanical energy is transferred by each wheel onboard of its respective same carriage, and is transformed into electric energy on the carriage to actuate the conveyor belt onboard of such carriage. A known solution of this type, which should allow sizing the current generators according to the mean power required, consists in using small generators that, drafted by the wheels, produce a small electric power, sufficient for charging batteries placed onboard of the same carriages. Such batteries will return the accumulated energy according to the sorting machine loading and unloading requirements, to satisfy wide possibilities of temporary overload.
However, batteries are heavy, polluting, expensive and have short life; moreover, they must be properly protected since they may be dangerous for the operators in the proximity of the sorting machine, should mechanical jamming occur in the sorting machine, caused by the transported items.
The present invention proposes a method according to which energy storage is not made in the batteries, but rather in the train of moving carriages. That is, use is made of the wide mechanical energy storage capacity possessed by the train itself, through its own kinetic energy.
The invention is implemented by an electricity generating device capable of drawingxe2x80x94according to the requirementsxe2x80x94all the necessary energy from said stored mechanical energy, and of converting it into electric energy for direct use, the electric energy produced by each electricity generating device being supplied to a plurality of, or even all, carriages of the machine.
A limited number of said devices is used, each comprising a wheel drafted and placed in rotation by friction against a fixed track, an alternator placed in rotation by said wheel through a mechanical connection, and an electronic control unit for adjusting and operating said generator. Said devices according to the invention are typically used in the number of one per every 30 carriages approximately. The devices are adapted to operate in parallel to power an electric distribution line to which the carriages of the sorting machine are connected.
Since such devices are limited in number, each of them should be capable of transferring a considerable power onboard of a plurality of the carriages, which above all in the step of current activation of many unloads, implies an intense braking stress for the drafted wheel. That is, electric power peaks place high electric energy demands on the alternators that, in turn, place high mechanical energy demands on the wheels, thereby placing high resistance (braking) to wheel rotation.
In order to prevent sliding of the drafted wheel while such strong power peaks are drawn, by reducing stresses to admissible values, a device has been developed, which is the object of concurrently filed commonly owned U.S. patent application Ser. No. [Attorney Docket No. 024445-297], corresponding to Italian Application No. MI 2002A 000786 filed Apr. 12, 2002, the disclosure of which is incorporated by reference. Reference shall therefore be made to it for the relevant description.